If you developed the App yourself [and have the Source Code] it depends on the tools you have used.

If you used Xcode all the way the App would be in Objective-C [which is hardly supported outside the Apple world] with Cocoa APIs [which are Apple only].
This means you would have to re-write the entire App.

If you used some other base (Java, C++) and some porting platform there might be a chance that there are tools to port it to other mobile platforms as well.